Why are there Strange Green Pipes growing from the ground?

Every once and awhile, there they are in front of
you, on a street or beside a park – green pipes about
8 inches in diameter and 3 to 12 feet tall, rising out
of the ground mysteriously. They don’t make a sound,
and most people don’t think they can detect an odour,
but do you ever wonder why they are there, and what
they do?

The taller green stacks are oftentimes paired with
shorter, candy cane–shaped ones, but eventually these
green pipes all lead to one place. Those that are part of
a ventilation stack for Toronto’s complex sewer system
known as the Mid Toronto Interceptor (MTI), all end
up at an underground chamber of sewage almost 100
feet underground.

Buried eighty to ninety feet, the MTI runs between
High Park and the Ashbridges Bay Treatment Plant.
But because the MTI is an
enclosed sewer system,
it requires street level
venting for non-toxic
methane gas that
collects underground.
Methane is a
colourless, odourless,
non toxic gas that is
lighter than air, so
it’s easy to collect and
direct into the atmosphere.

It is a natural by-product of the decomposition of
organic material by bacteria, in the absence of oxygen.
Methane production may occur wherever there is
decaying organic matter, for example in landfills,
swamps, and even in organic soils.

Exposure to methane gas does not pose a direct
health risk. However, this kind of passive venting
system and monitoring for methane gas is a safe and
necessary way that cities today control underground
gases. Such gases collect somewhere before they leak
into our air or worse still, accumulate and possibly
cause bigger problems.

The green stacks connected to the MTI are fitted
with a series of carbon filters, permit the circulation
of fresh air into the system and allow for fetid air to
exit. The filters are changed regularly.

Built in the late sixties and early seventies, the
MTI was constructed as a further means to prevent
untreated sewage from ending up in Lake Ontario.
The MTI collects sewer flows from across Toronto,
including from local municipal combined sewers,
flows diverted from two other interceptors (High
Level Interceptor HLI - and Low Level Interceptor
LLI) as well as sludge from the Humber Treatment
Plant. The MTI drains to the Ashbridges Bay

Treatment Plant Flows are controlled by sluice gates
(which act like valves) throughout the system. Gates
are located in underground chambers along the MTI
and along branches connecting to the HLI and LLI.
It gets confusing because there are additional green
pipes, which also aid in underground air circulation
and the ventilation of non toxic methane gas that is
being slowly released from underground landfill sites –
where there is decaying organic material.

In some US cities, you can find examples of “passive
venting” where a city has developed over a former
farm. In Toronto, you can find it along the edges of
various parks or green spaces that have been created
on a former landfill site or filled-in ravine. Riverdale
Park, for example, was built on a landfill site last
used in the 1920s. Many years later, around 1978,
a passive venting system – with those green pipes –
was installed along the eastern edge to safely vent the
continuous methane gases.

There are an estimated 15 green “pipe” stacks
connected to the MTI in Toronto, in addition to
the pipes placed along various parklands in the city.
Beaches Living invites anyone to go out and count
them!

Reference: City of Toronto,

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